It is recognized that the function of the tracheobronchial mucociliary epithelium is critical to the health and well being of the newborn infant. Still our understanding of the perinatal development of the airways is quite incomplete and we have a limited appreciation of how airway immaturity may contribute to pulmonary disease in the neonate. Whereas research over the past two decades has done much to improve our understanding of endocrine involvement in the maturation of the pulmonary surfactant system, no attention has been paid to the potential role that hormones or other materno-fetal factors may play in the fetal (and postnatal) development of the pulmonary airways epithelium. The proposed investigation will examine the influence that the hormones corticosterone, T3 and insulin play in the morphogenesis of the tracheal epithelium and submucosal mucous glands. This research will use organ culture under component defined serum-free media conditions to isolate and control the in vitro environment of fetal rat (and hamster) trachea explants. Morphological methods (TEM, SEM, LM, LM mucin histochemistry) will be used to analyze the ontogeny of airways cell types in vivo and in vitro. Morphometric analysis will quantitate the influence of corticosterone, T3 and insulin (administered separately and in combination) on the cytomorphogenesis of specific airways cell types. This investigation will greatly improve our understanding of endocrine influence in the morphogenetic development of key cell types involved in respiratory defense function in the neonate.